1. Field of the Invention
This invention relates to the field of microactuated hard disk drive suspensions. More particularly, this invention relates to the field of a wireless microactuator assembly for a hard disk drive suspension, and mechanical and electrical connections to the microactuator.
2. Description of Related Art
Storage of information has progressed through the years. From the early days, primitive man stored information on walls of caves, as well as used writings on wood such as bamboo. Since then, people have used wood, silk, and papers as a media for writings. Paper has been bound to form books. Information is now stored electronically on disks, tape, and semiconductor devices. As merely an example, some of the early disks used magnetic technology to store bits of information in a digital manner onto the magnetic media. One of the first disk drives was discovered in the 1950's by International Business Machines of Armonk, N.Y.]
Although such disks have been successful, there continues to be a demand for larger storage capacity drives. Higher storage capacity can be achieved in part by increasing an aerial density of the disk. That is, the density increases with the number of tracks per inch (TPI) and the number of bits per inch (BPI) on the disk.
As track density increases, however, the data track becomes narrower and the spacing between data tracks on the disk decreases. It becomes increasingly difficult for the motor and servo control system to quickly and accurately position the read/write head over the desired track. Conventional actuator motors, such as voice coil motors (VCM), often lack sufficient resolution and bandwidth to effectively accommodate high track-density disks. As a result, a high bandwidth and resolution second-stage microactuator is often necessary to precisely position the read/write head over a selected track of the disk for reading data from the disk and writing data to the disk. A suspension having such a second-stage microactuator is often referred to as a microactuated suspension or a dual stage actuator (DSA) suspension.
Microactuators for suspensions such as hard disk drive suspensions are typically piezoelectric devices, and more specifically, lead zirconate titanate (PZT). For simplicity of the following discussion, the term “PZT” will be used to refer in general to a piezoelectric device. U.S. Pat. No. 7,459,835 issued to Mei et al. shows a disk drive suspension having two PZT microactuators for the fine positioning of a read/write head over the desired track of a hard disk. U.S. Pat. No. 6,278,587 issued to Mei at all describes a microactuated suspension in which the microactuator is held to the load beam by interfitting structures. A common method of bonding PZTs to suspensions and electrically connecting to the PZTs is to apply a conductive epoxy on one surface of the PZT, thus providing both a mechanical and electrical bond between one polarity of the PZT and the stainless steel substrate of the suspension, and either a thermosonic or solder connection to the opposing surface of the PZT. U.S. Pat. No. 6,456,464 issued to Khan et al. describes a microactuated suspension in which the microactuator is mechanically and electrically bonded using a conductive adhesive such as a silver filled epoxy resin. U.S. Pat. No. 6,734,603 issued to Hellbaum et al. describes an interconnection technique that uses a high temperature polyimide adhesive. Typically, a first end of a wire lead referred to as a “tail weave” must be bonded to at least one of the PZT faces, such as by soldering, by conductive adhesive, or by thermosonic bonding, and the other end of the wire must be connected to the flexible circuit, sometimes called the “flex trace” or “flexure.”
FIG. 10 is a side perspective view of a prior art microactuated suspension. Two PZT elements 1002 and 1004 are affixed atop the suspension, with control voltages applied to the two PZTs through lead wires 1006. The result is that the magnetic read/write head mounted at the end of the load suspension moves back and forth in response to command voltages applied by the controller to the PZTs, so that the read/write head follows the desired data track on the disk. In the particular suspension shown, the two PZTs 1002 and 1004 have opposite polarity and therefore can be driven by a single voltage applied via a single wire 1006. Control wire 1006 is also bonded to bond pad 1010 of the flexible circuit to bring the control voltage to the PZTs. In other designs, the PZTs have the same polarity, and two separate control wires must be soldered or otherwise bonded to PZTs 1002 and 1004 on one end and to a bond pad 1010 on the other end. The control wires are sometimes referred to as a “tail weave.” The tail weave process is typically delicate and time consuming, thus adding a significant cost component to the finished suspension assembly.
A technique referred to as Thin Layer Unimorph Ferroelectric Driver and Sensor (“Thunder”) and described in U.S. Pat. Nos. 5,639,850, 6,060,811, and 5,632,841, involves laminating stainless steel, PZT, and aluminum using a high temperature adhesive, in order to pre-stress the structure upon cooling thereby giving the device a greater stroke distance.
One disadvantage to using a high temperature epoxy or other high temperature process to make mechanical and/or electrical connections to the PZT material is that upon cooling the PZT is under compression and is actually bowed due to the mismatches in coefficients of thermal expansion (CTE) between the stainless steel and the PZT. Although a pre-bowed PZT is claimed by the marketers of the Thunder process to provide increased stroke length, the temperature encountered in high temperature lamination results in a de-poling of the PZT. This de-poling reduces the effective stroke length of the device, or requires repoling as discussed in U.S. Pat. No. 6,734,603. However, because the PZT is physically constrained by its adhesion to the suspension during the re-poling process, in this constrained state the PZT will typically attain less than 80% of its original D31 displacement (Δ length).
A further disadvantage to using adhesive to bond the PZT to the stainless steel is that the adhesive bonding process generally not compatible with the clean room requirements for assembling disk drives. This is especially true when using conductive adhesives, which generally contain small metallic particles. The adhesive bonding process can produce small stray particles that can lead to product defects.